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// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_LOCK_H_
#define BASE_LOCK_H_
#include "base/lock_impl.h"
// A convenient wrapper for an OS specific critical section.
//
// NOTE: Although windows critical sections support recursive locks, we do not
// allow this, and we will commonly fire a DCHECK() if a thread attempts to
// acquire the lock a second time (while already holding it).
//
// Complication: UnitTest for DeathTests catch DCHECK exceptions, so we need
// to write code assuming DCHECK will throw. This means we need to save any
// assertable value in a local until we can safely throw.
class Lock {
public:
Lock();
~Lock();
void Acquire();
void Release();
// If the lock is not held, take it and return true. If the lock is already
// held by another thread, immediately return false.
bool Try();
// Return the underlying lock implementation.
// TODO(awalker): refactor lock and condition variables so that this is
// unnecessary.
LockImpl* lock_impl() { return &lock_; }
private:
LockImpl lock_; // User-supplied underlying lock implementation.
#ifndef NDEBUG
// All private data is implicitly protected by lock_.
// Be VERY careful to only access members under that lock.
int32 recursion_count_shadow_;
bool recursion_used_; // Allow debugging to continued after a DCHECK().
int32 acquisition_count_; // Number of times lock was acquired.
int32 contention_count_; // Number of times there was contention.
#endif // NDEBUG
DISALLOW_COPY_AND_ASSIGN(Lock);
};
// A helper class that acquires the given Lock while the AutoLock is in scope.
class AutoLock {
public:
explicit AutoLock(Lock& lock) : lock_(lock) {
lock_.Acquire();
}
~AutoLock() {
lock_.Release();
}
private:
Lock& lock_;
DISALLOW_COPY_AND_ASSIGN(AutoLock);
};
// AutoUnlock is a helper class for ConditionVariable that will Release() the
// lock argument in the constructor, and re-Acquire() it in the destructor.
class ConditionVariable;
class AutoUnlock {
private: // Everything is private, so only our friend can use us.
friend class ConditionVariable; // The only user of this class.
explicit AutoUnlock(Lock& lock) : lock_(&lock) {
// We require our caller to have the lock.
lock_->Release();
}
~AutoUnlock() {
lock_->Acquire();
}
Lock* lock_;
};
#endif // BASE_LOCK_H_
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